Telerobotics allows users to indirectly manipulate and interact with environments via master and slave robotic mechanisms. It enables operation at a distance and can also scale human forces and motions to achieve stronger, larger, or smaller interfaces. Applications range from space exploration to minimally invasive surgery. Vision is typically the dominant feedback modality in these systems, but the addition of haptic feedback provides more complete information to the user and can improve their ability to perform complex tasks.
High frequency feedback to a user is commonly recognized as vital to achieving a realistic telerobotic experience. However, high frequency feedback continues to be a challenge for most telerobotic systems. Difficulties such as contact instabilities have led researchers to sidestep stability issues using alternate modalities such as audio and vibrotactile displays.
Among the force feedback architectures, one could distinguish two existing philosophies. First, position-position approaches use slave tracking errors to feed back computed forces. Typically, they connect master and slave with a single PD controller imitating a spring and damper. This method is passive and provides robust stability without any knowledge of the environment. Furthermore, in this approach the critical high frequency forces are masked out of the feedback and the operator experiences a soft, compliant feel.
Realizing that human perception peaks at several hundred Hertz, the opposing philosophy utilizes a position-force architecture. It feeds measured contact forces directly back to the user, with high frequency signals intact. This violates passivity by hiding the slave's inertia and often has limited stability, especially in contact with stiff environments. Though researchers have tried to improve stability margins, these systems are fundamentally sensitive to lag and delays.
The presence of even small time delays, typically found in the communication channel between the master and slave sites, poses a serious stability problem for force feedback telerobots. Most delay capable controllers ultimately achieve stability through prediction across the delay and/or by severely restricting the bandwidth of the system. Prediction of interactions with a truly unknown environment itself proves problematic. Limiting the system bandwidth deprives the user of very important high frequency feedback information. Even wave variable controllers with guaranteed stability focus on low frequency interactions. For a description of wave variable controllers the reader is referred to Niemeyer et al. (Niemeyer G and Slotine J J E (2004), a paper entitled “Telemanipulation with time delays” and published in the International Journal of Robotics Research 23(9):873-890).
Accordingly, there is a need in the art to develop new methods and systems to overcome the shortcomings in the art and integrate high frequency feedback in telerobotic systems to enhance users' telerobotic experience.